The present invention relates to is organic resins or compounds resistant to temperature and polymerizing in bulk without evolution of volatile products.
Thermostable structures, their chemistry and their properties have been amply described in recent years (P. E. Cassidy, "Thermally Stable Polymers", Marcel Dekker, 1980, and J. P. Critchley, G. J. Knight, W. W. Wright, "Heat Resistant Polymers", Plenum Press 1983). These materials have applications in the industrial field in particular, such as electrotechnics, electronics, microelectronics or separation techniques. Thermoplastic thermostable polymers whose principal aromatic or heterocyclic chain is rendered more flexible by ether, sulfur, perfluoroisopropylidene or other bonds are singled out. These polymers can be used in solution or in bulk above the glass-transition temperature or above the melting temperature of their use as adhesives or composite matrices, for example.
Under these conditions, high pressures have to be applied and the thermal content of the material is limited by glass or crystalline transitions.
The second class of polymers investigated for structural applications is that of thermosetting polymers. Some are linear. They are used in the form of functional oligomers of low molecular weight and polycondensation is carried out under production conditions. This is the case for polybenzhydrolimides, described notably in FR-A-1 601 091 patent. The disadvantage with these resins is the evolution of volatile products during polycondensation.
This disadvantage is also encountered with PMR resins ("polymerization of monomeric reactants"), in particular those marketed under the name of PMR 15. These are mixtures obtained by condensation of a methyl diester of tetracarboxylic benzophenone acid, the methyl monoester of nadic acid and an aromatic diamine, such as 4,4-diamino diphenylmethane. The proportions of reactants are calculated such that the theoretical molecular weight of the product is about 1500 and so that all molecules end with nadic groups at each end. At the moment of implementation, condensation and imidation reactions are produced, then at the highest temperature (270.degree. C.), polymerization of reactive ends occurs, leading to reticulation of the system (T. T. Serafini, P. Delvigs, G. R. Lightsey, J. Appl. Polym. Sci., 16, 905, 1972).
These reactants are unstable at room temperature and are difficult to implement. This evolution towards thermostable thermosetting systems thus presents at least two considerable problems: the choice of chaining between the reactive functions and the choice of the two reactive end functions. Chaining between the reactive functions should not lead to evolution of volatile products during use and, consequently, must be completely condensed and/or cyclized. Furthermore, it is the nature of this chaining that will fix the emollescence point of the resin before reaction, as well as the glass-transition point of the network before reticulation.
Concerning the two reactive functions, three main groups can be distinguished: maleimide, nadimide and acetylene functions.
Acetylene functions polymerize at low temperatures: very slowly as from 150.degree. C. and rapidly at 200.degree. C.
Polymerization of maleimides greatly depends on the environment and three types of polycondensation are identified: polymerization by nucleophilic addition (Michael addition), radical polymerization, anionic polymerization. It is difficult to control implementation reactions and, when considering polycondensation by addition of a diamine, the presence of a free amine in the resin renders this type of material or questionable valve in view of legislation concerning toxicity. Polymerization of nadic groups involves a Diels-Adler retro reaction which liberates a maleimide function and a cyclopentadiene molecule. Production of this type of resin thus requires a delicate choice of temperature and pressure to be made so that the volatile diene is incorporated into the material by polymerization.
It is thus not surprising to find, for new thermostable resins, the choice of the reactive function oriented towards ethylene resins, despite a certain amount of difficulty in synthesis in introducing the acetylene function in the molecule. The resin Thermid 600 (marketed by National Starch) is an example of an oligoimide (or isoimide) ending in an ethylene function at each end. Nontheless, it must be noted that these resins melt at a temperature higher than the temperature at which polymerization of acetylenes begins. This is rather inconvenient as it would be difficult to wet the support, satisfactorialy without passing through the melted state.
The same is true for most quinoxaline resins ending in acetylene groups studied by NASA and called ATQ (U.S. Ser. No. 518,897 patent application or R. F. Kovar, G. F. L. Ehlers, F. E. Arnold, Poly. Prep. Am. Chem. Soc. Div. Polym. Chem. 16 (2) 246 1975).
This is, generally speaking, the disadvantage with most heterocyclic resins, which are intrinsically rigid. We have tried to overcome this difficulty by abandoning heterocyclic chaining in favor of ether sulfone type chainings. The resins obtained, called ATS, allow a fusible stage before reticulation of terminal acetylene groups (U.S. Pat. No. 4 131 625 patent and R. F. Kovar, G. F. L. Ehlers, F. E. Arnold, J. Poly. Sci., Polym. Chem. Ed. 15, 1981, 1977). On the other hand, the glass-transition temperature of the reticulated network is often low.